 /*******************************************************************************
  * Copyright (c) 2005, 2007 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui.internal.services;

 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.IEvaluationContext;
 import org.eclipse.ui.ISources;

 /**
  * <p>
  * A cache of the result of an expression. This also provides the source
  * priority for the expression.
  * </p>
  * <p>
  * This interface is not intended to be implemented or extended by clients.
  * </p>
  *
  * @since 3.2
  * @see org.eclipse.ui.ISources
  * @see org.eclipse.ui.ISourceProvider
  */
 public interface IEvaluationResultCache {

     /**
      * Clears the cached computation of the <code>evaluate</code> method, if
      * any. This method is only intended for internal use. It provides a
      * mechanism by which <code>ISourceProvider</code> events can invalidate
      * state on a <code>IEvaluationResultCache</code> instance.
      */
     public void clearResult();

     /**
      * Returns the expression controlling the activation or visibility of this
      * item.
      *
      * @return The expression associated with this item; may be
      * <code>null</code>.
      */
     public Expression getExpression();

     /**
      * Returns the priority that has been given to this expression.
      *
      * @return The priority.
      * @see ISources
      */
     public int getSourcePriority();

     /**
      * Evaluates the expression -- given the current state of the workbench.
      * This method should cache its computation. The cache will be cleared by a
      * call to <code>clearResult</code>.
      *
      * @param context
      * The context in which this state should be evaluated; must not
      * be <code>null</code>.
      * @return <code>true</code> if the expression currently evaluates to
      * <code>true</code>; <code>false</code> otherwise.
      */
     public boolean evaluate(IEvaluationContext context);

     /**
      * Forces the cached result to be a particular value. This will <b>not</b>
      * notify any users of the cache that it has changed.
      *
      * @param result
      * The cached result to use.
      * @since 3.3
      */
     public void setResult(boolean result);
 }

